U.S. patent number 4,647,917 [Application Number 06/593,146] was granted by the patent office on 1987-03-03 for article control system having coded magnetomechanical marker.
This patent grant is currently assigned to Allied Corporation. Invention is credited to Philip M. Anderson, III, Jeffrey C. Urbanski.
United States Patent |
4,647,917 |
Anderson, III , et
al. |
March 3, 1987 |
Article control system having coded magnetomechanical marker
Abstract
An article control system has an encoded marker associated with
an article appointed for passage through an interrogation zone. The
marker resonates upon interrogation to provide a signal which is
detected and compared against a code list containing at least one
predefined code. A signal generated upon verification of parity
between marker resonance and the predefined code triggers an alarm
or actuates a gating mechanism adapted to redirect the article.
Inventors: |
Anderson, III; Philip M.
(Chatham, NJ), Urbanski; Jeffrey C. (Sparta, NJ) |
Assignee: |
Allied Corporation (Morris
Township, Morris County, NJ)
|
Family
ID: |
24373567 |
Appl.
No.: |
06/593,146 |
Filed: |
March 26, 1984 |
Current U.S.
Class: |
340/572.4;
148/304; 148/307; 148/310; 148/311; 148/403; 235/384; 340/572.7;
340/572.8 |
Current CPC
Class: |
G06K
7/086 (20130101); G06K 19/0672 (20130101); G08B
13/2474 (20130101); G08B 13/2462 (20130101); G08B
13/2471 (20130101); G08B 13/2408 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G06K 7/08 (20060101); G06K
19/067 (20060101); G08B 013/18 () |
Field of
Search: |
;340/572,551 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Swann, III; Glen R.
Attorney, Agent or Firm: Buff; Ernest D. Fuchs; Gerhard
H.
Claims
What is claimed is:
1. An article control system, comprising:
(a) a means for defining an interrogation zone;
(b) generating means for generating within said interrogation zone
a magnetic field having a predetermined frequency band, said
generating means including an interrogating coil;
(c) a marker associated with an article appointed for passage
through said interrogation zone, said marker being responsive
within said interrogation zone to undergo a substantial change in
its effective magnetic permeability at preselected frequencies
within said frequency band, which provides the marker with signal
identity, said marker comprising at least one strip of
magnetostrictive, ferromagnetic material that is at least 50
percent amorphous, said strip being adapted to be magnetically
biased and thereby armed to resonate mechanically at a frequency
within the frequency band of said magnetic field;
(d) a detecting means for detecting resonance of said marker within
said interrogation zone;
(e) cataloging means for maintaining a code list comprising at
least one predefined code;
(f) code entry means for generating said code list;
(g) decoding means for comparing said detected marker resonance
against said code list to verify parity between said resonance and
said predefined code; and
(h) signal means for generating a signal in response to an
indication of parity from said decoding means.
2. An article control system as recited in claim 1, wherein said
signal is an audible or visible alarm.
3. An article control system as recited in claim 1, wherein said
signal is an electronic signal and said system further comprises
gating means for redirecting said article in response to said
electronic signal.
4. An article control system as recited in claim 3 wherein said
code list comprises a plurality of predefined codes, said decoding
means comprises means for verifying parity between said resonance
and one of said predefined codes, and said gating means comprises a
plurality of gates, each of said gates being actuated by said
signal means in response to parity with a different one of said
predefined codes.
5. An article control system as recited in claim 1, wherein said
code entry means is a electronic signal decoder.
6. An article control system, as recited in claim 1, wherein each
of said generating and said detecting means includes at least one
antenna coil.
7. An article control system as recited 6, wherein said antenna
coils are disposed on opposing sides of said interrogation
zone.
8. An article control system, as recited in claim 6, wherein said
antenna coils of said generating and said detecting means are
coplanar
9. An article control system as recited in claim 1, wherein said
generating means comprises a pair of antenna coils disposed
adjacent and coplanar to each other and driven by said generating
means alternatively at phase angles of 0.degree. and 180.degree.
with respect to each other.
10. An article control system as recited in claim 1, wherein said
generating means includes frequency sweeping means adapted to sweep
through each different preselected frequency of said markers.
11. An article control system as recited in claim 1, wherein said
generating means includes energizing means adapted to provide said
interrogating coil with a burst of sine wave frequencies that
includes each said different preselected frequency.
12. An article control system as recited in claim 1, wherein said
generating means includes energizing means adapted to provide said
interrogating coil with a pulse, the width of which is equal to
1/(2 fr), where fr is the preselected frequency.
13. An article surveillance system as recited in claim 1, wherein
said magnetostrictive ferromagnetic material of said marker is at
least 80 percent amorphous.
14. An article control system, as recited in claim 1, wherein said
magnetostrictive ferromagnetic material of said marker has a
composition consisting essentially of the formula M.sub.a N.sub.b
O.sub.c X.sub.d Y.sub.e Z.sub.f, where M is at least one of iron
and cobalt, N is nickel, O is at least one of chromium and
phosphorous, X is at least one of boron and phosphorous, Y is
silicon, Z is carbon, "a"-"f" are in atom percent, "a" ranges from
about 35-85, "b" ranges from about 0-45, "c" ranges from about 0-7,
d ranges from about 5-22, "e" ranges from about 0-15, f ranges from
about 0-2, and the sum of d+e+f ranges from about 15-25.
15. An article control system, comprising:
(a) a means for defining an interrogation zone;
(b) generating means for generating within said interrogation zone
a magnetic field having a predetermined frequency band, said
generating means including an interrogating coil and an energizing
means adapted to provide said interrogating coil with a burst of
noise;
(c) a marker associated with an article appointed for passage
through said interrogation zone, said marker being responsive
within said interrogation zone to undergo a substantial change in
its effective magnetic permeability at preselected frequencies
within said frequency band, which prevides the marker with signal
identity, said marker comprising at least one strip of
magnetostrictive, ferromagnetic material, said strip being adapted
to be magnetically biased and thereby armed to resonate
mechanically at a frequency within the frequency band of said
magnetic field;
(d) a detecting means for detecting resonance of said marker within
said interrogation zone;
(e) cataloging means for maintaining a code list comprising at
least one predefined code;
(f) code entry means for generating said code list;
(g) decoding means for comparing said detected marker resonance
against code list to verify parity between said resonance and said
predefined code; and
(h) signal means for generating a signal in response to an
indication of parity from said decoding means.
16. An article control system, comprising:
(a) a means for defining an interrogation zone;
(b) generating means for generating within said interrogation zone
a magnetic field having a predetermined frequency band, said
generating means including an interrogating coil and an energizing
means adapted to provide said interrogating coil with a burst of
sine wave frequency;
(c) a marker associated with an article appointed for passage
through said interrogation zone, said marker being responsive
within said interrogation zone to undergo a substantial change in
its effective magnetic permeability at preselected frequencies
within said frequency band, which provides the marker with signal
identity, said marker comprising at least one strip of
magnetostrictive, ferromagnetic material, said strip being adapted
to be magnetically biased and thereby armed to resonate
mechanically at a frequency within the frequency band of said
magnetic field;
(d) a detecting means for detecting resonance of said marker within
said interrogation zone;
(e) cataloging means for maintaining a code list comprising at
least one predefined code;
(f) code entry means for generating said code list;
(g) decoding means for comparing said detected marker resonance
against said code list to verify partiy between said resonance and
said predefined code; and
(h) signal means for generating a signal in response to an
indication of parity from said decoding means.
17. An article control system, comprising:
(a) a means for defining an interrogation zone;
(b) generating means for generating within said interrogation zone
a magnetic field having a predetermined frequency band, said
generating means including an interrogating coil and an energizing
means for providing said interrogating coil with an energizing
signal;
(c) a marker associated with an article appointed for passage
through said interrogation zone, said marker being responsive
within said interrogation zone to undergo a substantial change in
its effective magnetic permeability at preselected frequencies
within said frequency band, which provides the marker with signal
identity, said marker comprising at least one strip of
magnetostrictive, ferromagnetic material, said strip being adapted
to be magnetically biased and thereby armed to resonate
mechanically at a frequency within the frequency band of said
magnetic field;
(d) a detecting means for detecting resonance of said marker with
said interrogation zone, said detecting means including receiving
means for distinguishing a resonant frequency for each of said
markers detected by said receiving coil from other frequencies
induced therein;
(e) synchronizing means associated with said energizing means for
sequentially activating and deactivating each of said energizing
means and receiving means;
(f) cataloging means for maintaining a code list comprising at
least one predefined code;
(g) code entry means for generating said code list;
(h) decoding means for comparing said detected marker resonance
against said code list to verify parity between said resonance and
said predefined code; and
(i) signal means for generating a signal in response to an
indication of parity from said decoding means.
18. An article control system as recited in claim 17, wherein said
synchronizing means is adapted to prevent activation of said
receiving means for substantially the entire period of time that
said energizing means is activated.
19. An article control system as recited in claim 17, wherein said
synchronizing means is adapted to prevent activation of said
energizing means for substantially the entire period of time that
said receiving means is activated.
20. An article control system, comprising:
(a) a means for defining an interrogation zone;
(b) generating means for generating within said interrogation zone
a magnetic field having a predetermined frequency band, said
generating means including an interrogating coil;
(c) a marker associated with an article appointed for passage
through said interrogation zone, said marker being responsive
within said interrogation zone to undergo a substantial change in
its effective magnetic permeability at preselected frequencies
within said frequency band, which provides the marker with signal
identity, said marker comprising at least one strip of
magnetostrictive, ferromagnetic material, said strip being adapted
to be magnetically biased and thereby armed to resonate
mechanically at a frequency within the frequency band of said
magnetic field, and said marker being comprised of a ferromagnetic
filled plastic in the form of a container consisting of two parts:
a boat and cover, which upon being magnetized is adapted to provide
said strips with a magnetic bias field;
(d) a detecting means for detecting resonance of said marker within
said interrogation zone;
(e) cataloging means for maintaining a code list comprising at
least one predefined code;
(f) code entry means for generating said code list;
(g) decoding means for comparing said detected marker resonance
against said code list to verify parity between said resonance and
said predefined code; and
(h) signal means for generating a signal in response to an
indication of parity from said decoding means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an article control system and an encoded
marker used therein, and more particularly, to a system in which an
article of luggage having an encoded marker attached thereto is
monitored from a remote location and thus guided to a proper
destination.
2. Description of the Prior Art
Article control systems, upon which this invention has improved,
are conventionally employed in applications where articles of
luggage are required to be transferred to many different locations.
There presently exists two main categories of such systems: manual
and automated.
Manual article control systems entail affixing a label containing a
destination code and/or address directly to an article and
thereafter visually reading the affixed label to determine the
proper routing required to allow the article to reach its proper
destination. Such systems are personnel dependent, thus in
applications where large volumes of articles are transferred to
many different locations human error or misreading of labels
becomes increasingly detrimental to the efficiency of the system.
Also, visually reading the affixed label requires correct
positioning and the proper lighting of the article.
Existing automated article control systems entail affixing a color
coded tag or bar code to an article, such tags or bar codes contain
inscripted information about the article such as a name, address or
destination. An article to which a tag or bar code is affixed upon
passing by a visual scanner conveys its inscripted information to a
signal generating device enabling a routing mechanism to guide the
article to its proper destination. The major drawbacks of these
tags or codes is that they require proper orientation of the color
coded tag or bar code to the visual scanner and any obstruction
between the tag or code and the scanner disables the system. As a
result of this such automated article control system are less
efficient and reliable than expected.
SUMMARY OF THE INVENTION
The present invention provides an article control system that
allows an article to which an encoded marker is attached to be
remotely monitored and/or guided to a proper destination. The coded
marker remains functional regardless of the orientation of the
article to which it is attached and, more surprisingly, the marker
requires no power or physical contact with the system's sensing
devices.
Generally stated, the article control system of the invention
comprises means for defining an interrogation zone. The system has
a generating means, including an interrogating coil, for generating
a magnetic field having a frequency band within the interrogation
zone and a marker associated with an article appointed for passage
through the interrogation zone. The marker is responsive within the
interrogation zone to undergo a substantial change in its effective
magnetic permeability at preselected frequencies within the
frequency band that provides the marker with signal identity. The
marker comprises at least one strip of magnetostrictive,
ferromagnetic material. The strip is adapted to be magnetically
biased and thereby armed to resonate mechanically at a preselected
frequency with the frequency band of the magnetic field. The system
has a detecting means for detecting the resonance of the marker
within the interrogation zone. A cataloging means is provided for
maintaining a code list comprising at least one predefined code,
which is generated by a code entry means.
The system also includes a decoding means for comparing the
detected marker resonance against the code list to verify parity
between said resonance and said predefined code. Finally the system
entails a signal means for generating a signal in response to an
indication of parity from the decoding means
In addition to monitoring articles and/or guiding articles to a
proper destination, the article control system of the invention
provides added security against theft and/or accidental loss of
articles as a benefit of having a remotely detected marker whose
code is not externally visible.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood and further advantages
will become apparent when reference is made to the following
detailed description of the preferred embodiment of the
accompanying drawings in which:
FIG. 1 is a block diagram of an article surveillance system
incorporating the present invention;
FIG. 2 is a diagrammatic illustration of a typical installation of
the system of FIG. 1;
FIG. 3 is a graph showing the voltage induced by magnetomechanical
energy exchange of an article control marker over a preselected
frequency range;
FIG. 4 is a isometric view showing components of a marker adapted
for use in the system of FIG. 1;
FIG. 5 is an isometric view showing a portable unit of the system
of FIG. 1; and
FIG. 6 is a schematic electrical diagram of an interrogation and
detection scheme comprising part of the article control system of
FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The components of the article control system 10 can be fabricated
in a number of diverse sizes and configurations. As a consequence,
the invention has been found to function with many varieties of
article control systems. For illustrative purposes, the invention
is described in connection with an article control system in which
the monitored and/or guided articles are items of luggage passing
through an airport to which coded markers have been attached
allowing more efficient and reliable transferring of such items to
their proper destinations. It will be readily appreciated that the
invention can be employed for similar and yet diversified uses,
such as the identification of articles, wherein the marker and the
system exchange magnetomechanical energy so that the marker
functions as an identifier for checkpoint control of classified
documents, warehouse packages, library books and the like.
Accordingly, the invention is intended to encompass modifications
of the preferred embodiment wherein at least one resonant frequency
of the marker provides articles bearing it with signal
identity.
Referring to FIG. 1 of the drawings, there is shown an article
control system 10 responsive to the presence of an article within
an interrogation zone. The system 10 has means for defining an
interrogation zone 12. A field generating means 14 is provided for
generating a magnetic field having a frequency band within the
interrogation zone 12. The system 10 provides a marker 16
associated with an article 17 which is responsive within the
interrogation zone 12 to undergo a substantial change in its
effective magnetic permeability at preselected frequencies within
the frequency band that provides the marker 16 with signal
identity. A detecting means 20 is also provided for detecting
resonance of said marker within the interrogation zone 12. A
cataloging means 210 is provided for maintaining a code list
comprising at least one predefined code which is generated by a
code entry means 200. The system 10 also includes a decoding means
15 for comparing the detected marker resonances against the code
list to verify parity between said resonances and said predefined
code. Finally, the system entails a signal means 220 for generating
a signal in response to an indication of parity from the deooding
means 15.
FIG. 2 of the drawings is a diagrammatic illustration of an article
control system installed in an airport where incoming articles 17
labeled luggage from passengers must be monitored and/or guided to
the proper airplane whose destination matches that of the
passenger. A passenger and luggage 17 arrive at an airport and
proceed to the reservation desk 70. The reservation desk 70 is that
local at which the passenger's flight reservations are confirmed
and the luggage 17 is prepared for transit to the airplane's
luggage compartment. Upon verification of the passenger's
reservations a marker 16 is attached to the luggage 17. The code of
marker 16 is then entered via code entry means 200 to the
cataloging means 210, which correlates the entered code with the
passenger's name and destination. The luggage 17 with attached
marker 16 is then placed on conveyor 230, which transports luggage
17 towards the airplane cargo loading area. As shown in FIG. 2, the
main conveyor belt 230 proceeds past three gates A, B and C which
are connected to individual conveyor belts A (not shown), B and C,
each of which leads to a different airplane cargo loading area A
(not shown), B or C. The generating means 14, interrogating coil 72
and a receiving coil 74 of the detecting means 20 are located on
opposite sides of the conveyor belt 230 providing an interrogation
zone 12 located prior to the first gate C. The marker 16 upon
entering the interrogation zone 12 is characterized by a
substantial change in its effective magnetic permeability at the
resonant and/or antiresonant frequency (shown in FIG. 3 as fr and
fa) of which each of the predefined frequencies are comprised that
provides marker 16 with signal identity. The detecting means 20
then detects the resonant frequencies at which the marker 16
undergoes the substantial change in effective magnetic
permeability. These frequencies are then relayed to the decoding
means 15 which compares the detected marker 16 resonances against a
code list relayed from the cataloging means 210 and upon finding a
predefined code that matches the marker's 16 resonances, the
decoding means 20 relays a corresponding code from the code list to
the signal means 220 (FIG. 1). The signal means 220 is a series of
three gates A, B and C, each of which responds by opening to a
different code relayed from the decoding means 15. Thus, the
luggage 17, upon passing through the interrogation zone 12, is
guided through one of the gates A, B and C which corresponds to the
marker 16 code. Once the luggage 17 is through the correct gate,
the gate closes allowing the signal means 220 to respond to the
next code received from the decoding means 15. The luggage 17, upon
being guided through the correct gate, proceeds down a
corresponding conveyor A, B or C towards a corresponding airplane
cargo loading area A, B or C.
The marker 16 (FIG. 4) is comprised of at least one strip 18 of
amorphous magnetostrictive ferromagnetic material enclosed within a
container 19 composed of a ferromagnetic filled plastic such as
polyester filled with barium ferrite. Container 19 consists of two
parts: a boat 62 and a cover 44. The container must be constructed
in such a manner that strip 18 remains undamped or free to vibrate,
upon being placed in the boat 62 and enclosed by the cover 44. This
can be accomplished by leaving 1 millimeter clearance on all inside
dimensions of container 19. The container 19 is adapted, upon being
magnetized, to magnetically bias the strip 18 and thereby arm the
strip 18 to resonate at its preselected frequency. The marker is
composed of a magnetostrictive amorphous metal alloy in the form a
strip 18 having a first component composed of a composition
consisting essentially of the formula M.sub.a N.sub.b O.sub.c
X.sub.d Y.sub.e Z.sub.f, where M is at least one of iron and
cobalt, N is nickel, O is at least one of chromium and molybdenum,
X is at least one of boron and phosphorous, Y is silicon, Z is
carbon, "a"-"f" are in atom percent, "a" ranges from about 35-85,
"b" ranges from about 0-45, "c" ranges from about 0-7, "d" ranges
from about 5-22, "e" ranges from about 0-15 and "f" ranges from
about 0-2, and the sum of d+e+f ranges from about 15-25. The marker
16 is designed in such a manner as to allow numerous codes to be
represented. Coded markers having the structure of marker 16 are
visually indistinguishable from one another improving the system's
theft protection characteristics.
The code entry means 200 for generating a code list can be actuated
by several different methods. One method consists of a keyboard
wherein the code is visually read from markings on the marker 16
and then entered by pressing corresponding buttons on the keyboard
in the correct sequence. Alternatively the marker's 16 code may be
entered by voice demodulation in which markings on the marker 16
are transposed to verbal communication and then demodulated to an
electronic representation. Also an electronic signal such as that
created by detecting the resonances of marker 16 or by
communication via a modem can be used to enter the markers
code.
The cataloging means 210 for maintaining a code list, correlates
the code of marker 16 to information on the luggage 17 to which it
is attached such as destination code, identification codes and/or
routing codes. The cataloging means 210 receives the markers 16
code from the code entry means 200 and upon verification of the
passengers reservations the additional information codes are
received via an electronic terminal. Upon request the cataloging
means 210 transmits the code list to the decoding means 15 via an
electronic signal.
The decoding means 15 searches the code list, from the cataloging
means 210, for a code that matches the detected marker's 16 code,
from the detecting means 20. Upon finding a matching pair of codes
the decoding means 15 transmits a corresponding code such as a
destination code to the signal means 220. The signal means 220 then
produces a physical response which is individually keyed to the
received code such as opening a specific gate and/or lighting
corresponding lights.
The generating means 14 is comprised of an energizing circuit 201
(FIG. 6) and an interrogation coil 206. The energizing circuit 201
in the preferred embodiment is adapted to provide the interrogating
coil 206 with a burst of sine wave frequencies that includes each
the marker's preselected frequencies. There are several other
possible energizing means which provide the marker 16 with each of
its preselected frequencies, including (1) a frequency sweeping
means adapted to sweep through each different preselected frequency
of the marker 16, (2) an energizing means adapted to provide the
interrogating coil 206 with a pulse, the width of which is equal to
1/(2 fr), where fr is the preselected frequency (3) an energizing
means adapted to provide the interrogating coil 206 with a burst of
noise and (4) an energizing means adapted to provide the
interrogation coil 206 with a burst of sweeping sine wave
frequency.
In operation, the generating means 14 provides a burst of sine wave
frequencies. Upon completion of the burst the marker 16 will
continue to vibrate and thereby undergo damped oscillation at its
resonance frequencies. The vibrating marker 16 will cause a voltage
to be induced in the receiving coil 207 of the detection means 20
at each of the resonant frequencies. The detecting means 20 is
synchronized with the generating means 14 via synchronizing circuit
209 in such a manner as to allow the resonant frequencies induced
in the receiving coil 207 to be detected only after completion of
the interrogating burst. The detecting means 20 determines the
values, via the detecting circuit 202, of the resonant frequencies
of the marker 16 and thus produces a frequency code. The frequency
code is transmitted to the decoding means 15 for comparison with
the code list.
In another aspect of the invention, the article control system 5 in
FIG. 5 is designed as a portable unit capable of locating a
specific item of luggage located in the presence of many other
items of luggage. The method of operation is the same as previously
described, however, the configuration is slightly altered. The
antenna system 340 of FIG. 5 is constructed as a hand held unit
consisting of a pair of interrogation coils 350, 351 disposed
adjacent and coplanar to each other and driven alternately at phase
angles of 0.degree. and 180.degree. with respect to each other. A
receiving coil 352 is positioned coplanar and centered about the
interrogation coils 350, 351. The complete antenna system 340 is
encased within a nonmagnetic binder with an attached handle through
which linking means with the electronics of system 5 are placed.
The electronics of system 5 are located within a portable box which
enables the code of the specific luggage to be entered via a keypad
363 thereon. Upon positioning the antenna system 340 in the
vicinity of the specific luggage a signal is produced such as a
flashing light, 370. Thus system 5 enables a desired item of
luggage with affixed marker to be located efficiently and
quickly.
It has been found that markers 16 containing strips 18, or
magnetostrictive amorphous material are particularly adapted to
resonate mechanically at preselected frequencies of an incident
magnetic field. While we do to wish to be bound by any theory, it
is believed that, in markers of the aforesaid composition, direct
magnetic coupling between an ac magnetic field and the marker 16
occurs by means of the following mechanism.
When a ferromagnetic material such as an amorphous metal ribbon is
in a magnetic field (H), the ribbon's magnetic domains are caused
to grow and/or rotate. This domain movement allows magnetic energy
to be stored, in addition to a small amount of energy which is lost
as heat. When the field is removed, the domains return to their
original orientation releasing the stored magnetic energy, again
minus a small amount of energy lost as heat. Amorphous metal have
high efficiency in this mode of energy storage. Since amorphus
metals have no grain boundaries and have high resistivities, their
energy losses are extraordinarily low.
When the ferromagnetic ribbon is magnetostrictive, an additional
mode of energy storage is also possible. In the presence of a
magnetic field, a magnetostrictive amorphous metal ribbon will have
energy stored magnetically as described above but will also have
energy stored mechanically via magnetostriction. This mechanical
energy stored can be quantified as U.sub.e =(1/2) TS where T and S
are the stress and strain on the ribbon. This additional mode of
energy storage may be viewed as an increase in the effective
magnetic permeability of the ribbon.
When an ac magnetic field and a dc field are introduced on the
magnetostrictive ribbon (such as can be generated by ac and dc
electric currents in a solenoid), energy is alternately stored and
released with the frequency of the ac field. The magnetostrictive
energy storage and release are maximal at the material's mechanical
resonance frequency and minimal at its anti-resonance. This energy
storage and release induces a voltage in a pickup coil via flux
density changes in the ribbon. The flux density change may also be
viewed as an increase in effective magnetic permeability at the
resonant frequency and a decrease at antiresonance, thus, in
effect, increasing or decreasing, respectively, the magnetic
coupling between the driving solenoid and a second pickup solenoid.
The voltage induced by the purely magnetic energy exchange is
linear with frequency and the change in voltage with frequency is
small over a limited frequency range. The voltage induced by the
magnetomechanical energy exchange is also linear with frequency
except near mechanical resonance. For a thin ribbon the mechanical
resonance frequency is given by:
where L, E and D are the length, Youngs modulus and mass density of
the ribbon and n indicates the order of the harmonic. Therefore,
when the frequency of the ac magnetic field is swept around fr, a
characteristic signature is generated. The resonance peak is
closely followed by an anti-resonance peak shown in FIG. 3. This
anti-resonant peak occurs when the mechanical energy stored is near
zero.
The transfer of magnetic and mechanical energy described above is
called magnetomechanical coupling (MMC), and can be seen in all
magnetostrictive materials. The efficiency of this energy transfer
is proportional to the square of the magnetomechanical coupling
factor (k), and is defined as the ratio of mechanical to magnetic
energy. Phenomenologically, k is defined as ##EQU1## where fr and
fa are, respectively, the resonant and anti-resonant frequencies
described above. The larger the k factor, the greater the voltage
difference between resonant peak and anti-resonant valley. Also,
the larger the k, the larger the difference in frequency between
resonance and anti-resonance. Therefore, a large k facilitates the
observation of the MMC phenomena.
Coupling factors are influenced in a given amorphous metal by the
level of bias field present, the level of internal stress (or
structural anisotropy) present and by the level and direction of
any magnetic anisotropy. Annealing an amorphous metal relieves
internal stresses, thus enhancing k. The structural anisotropy is
small due to the ribbon's amorphous nature, also enhancing k.
Annealing in a properly oriented magnetic field can significantly
enhance coupling factors. Domain movement can be maximized when the
ribbon has a magnetic anisotropy which is perpendicular to the
interrogating field. Because of demagnetizing field effects, it is
practical to interrogate the ribbon only along its length (this
being the longest dimension). Therefore, the induced magnetic
anisotropy should be transverse to the long dimension of the
ribbon.
Maximum values of k are obtained by annealing the ribbon in a
saturating magnetic field which is perpendicular to ribbon length
(cross-field annealed). For a 1/2 inch ribbon, a field of a few
hundred oersted is required. The optimum time and temperature of
the anneal depends on the alloy employed. As an example, an
iron-boron-silicon alloy yields an optimum coupling (k>0.90)
when cross-field annealed at 400.degree. C. for 30 minutes. This
anneal yields an optimum bias field of 1 Oe. For alloys having the
compositions specified hereinabove, the annealing temperature
ranges from about 300.degree. to 450.degree. C. and the annealing
time ranges from about 7 to 120 min.
The anneal also affects the bias field required to optimize k. For
a given amorphous metal with a given anneal, the coupling depends
strongly on the bias field. At zero and saturating fields, the
coupling is zero (no resonant and anti-resonant phenomena). For a
given alloy, an optimum bias field exists which yields a maximum k.
For alloys having the compositions specified herein, the bias field
required to optimize k ranges from about 0.1 to 20 Oe.
Even though most magnetostrictive materials will exhibit some MMC,
amorphous metals yield extremely high coupling factors, and are,
therefore highly preferred. As-cast amorphous metals yield higher k
than most other magnetostrictive materials. No material has higher
k than amorphous metals when cross-field annealed. Amorphous metals
have high k because they have:
(a) low magnetic losses (no grain boundries, high resistivity), (b)
low structural and stress anisotropy, (c) reasonable
magnetostriction and (d) can be given a beneficial magnetic
anisotropy.
Amorphous metal alloys make good markers because (a) they have high
k--even as-cast, (b) they are mechanically strong, tough and
ductile, (c) they require low bias fields and (d) they have
extremely high magnetostrictivity (they develop a large force upon
resonating and are, therefore, more difficult to damp out). It will
be appreciated, therefore, that the amorphous metals of which the
marker of this invention is composed need not be annealed, but may
be incorporated into the marker "as cast".
Examples of amorphous ferromagnetic marker compositions in atomic
percent within the scope of the invention are set forth percent
within the scope of the invention are set forth below in Table
1.
TABLE 1 ______________________________________ ALLOY AS-CAST k
OPTIMAL ANNEALED k ______________________________________ Fe.sub.78
Si.sub.9 B.sub.13 0.35 >0.90 Fe.sub.79 Si.sub.5 B.sub.16 0.31
>0.90 Fe.sub.81 B.sub.13.5 Si.sub.3.5 C.sub.2 0.22 >0.90
Fe.sub.67 Co.sub.18 B.sub.14 Si.sub.1 0.45 0.72 Fe.sub.40 Ni.sub.38
Mo.sub.4 B.sub.28 0.23 0.50
______________________________________
Examples of amorphous metals that have been found unsuitable for
use as article surveillance system markers are set forth in Table
2.
TABLE 2 ______________________________________ COMPOSITION PERCENT
EXAMPLE 1 EXAMPLE 2 ______________________________________ Ni at. %
71.67 Ni at. % 65.63 wt. % 84.40 wt. % 76.97 Cr at. % 5.75 Cr at. %
11.55 wt. % 6 wt. % 12.0 B at. % 2.75 B wt. % 11.58 wt. % 2.75 wt.
% 2.5 Si at. % 7.10 Si at. % 7.13 wt. % 4 wt. % 4 Fe at. % 2.23 Fe
at. % 3.14 wt. % 2.5 wt. % 3.5 C at. % .25 C at. % .12 P at. % .032
P at. % -- wt. % .02 wt. % -- S at. % .031 S at. % -- wt. % .02 wt.
% -- Al at. % .093 Al at. % -- wt. % .05 wt. % -- Ti at. % .052 Ti
at. % -- wt. % .05 wt. % -- Zr at. % .027 Zr at. % -- wt. % .05 wt.
% -- Co at. % .085 Co at. % .85 wt. % .1 wt. % 1.0
______________________________________
The amorphous ferromagnetic metal marker of the invention is
prepared by cooling a melt of the desired composition at a rate of
at least about 10.sup.5 .degree. C./sec, employing metal alloy
quenching techniques well-known to the amorphous metal alloy art;
see, e.g., U.S. Pat. No. 3,856,513 to Chen et al. The purity of all
compositions is that found in normal commercial practice.
A variety of techniques are available for fabricating continuous
ribbon, wire, sheet, etc. Typically, a particular composition is
selected, powders or granules of the requisite elements in the
desired portions are melted and homogenized, and the molten alloy
is rapidly quenched on a chill surface, such as a rapidly rotating
metal cylinder.
Under these quenching conditions, a metastable, homogeneous,
ductile material is obtained. The metastable material may be
amorphous, in which case there is no long-range order. X-ray
diffraction patterns of amorphous metal alloys show only a diffuse
halo, similar to that observed for inorganic oxide glasses. Such
amorphous alloys show only a diffuse halo, similar to that observed
for inorganic oxide glasses. Such amorphous alloys must be at least
50% amorphous to be sufficiently ductile to permit subsequent
handling, such as stamping complex marker shapes from ribbons of
the alloys without degradation of the marker's signal identity.
Preferably, the amorphous metal marker must be at least 80%
amorphous to attain superior ductility.
The metastable phase may also be a solid solution of the
constituent elements. In the case of the marker of the invention,
such metastable, solid solution phases are not ordinarily produced
under conventional processing techniques employed in the art of
fabricating crystalline alloys. X-ray diffraction patterns of the
solid solution alloys show the sharp diffraction peaks
characteristic of crystalline alloys, with some broadening of the
peaks due to desired fine-grained size of crystallites. Such
metastable materials are also ductile when produced under the
conditions described above.
Having thus described the invention in rather full detail, it will
be understood that such detail need not be strictly adhered to but
that various changes and modifications may suggest themselves to
one skilled in the art, all falling within the scope of the
invention as defined by the subjoined claims.
* * * * *